import { useEffect, useState } from "react";

/**
 * Returns the last value of type T that passes a filter function
 * @param value changing value
 * @param filterFn function that determines whether a given value should be considered for the last value
 */
export default function useLast<T>(
  value: T | undefined | null,
  filterFn?: (value: T | null | undefined) => boolean
): T | null | undefined {
  const [last, setLast] = useState<T | null | undefined>(
    filterFn && filterFn(value) ? value : undefined
  );
  useEffect(() => {
    setLast((last) => {
      const shouldUse: boolean = filterFn ? filterFn(value) : true;
      if (shouldUse) return value;
      return last;
    });
  }, [filterFn, value]);
  return last;
}

function isDefined<T>(x: T | null | undefined): x is T {
  return x !== null && x !== undefined;
}

/**
 * Returns the last truthy value of type T
 * @param value changing value
 */
export function useLastTruthy<T>(
  value: T | undefined | null
): T | null | undefined {
  return useLast(value, isDefined);
}